This invention relates to a method of performing dental procedures, and more particularly, to a method of performing orthodontic procedures and a device useful in performing some of those procedures.
Orthodontic cases are generally divided into two categories according to the direction in which the major tooth movements are made to straighten the teeth. The first category will be referred to as expansion cases. In expansion cases the crowded and crooked teeth are moved toward the periphery of the outline of the jawbone to make room for them. The second category will be referred to as retraction cases. In retraction cases generally one or more teeth are removed to create more room in the jaw for the teeth that remain. To line them up straight, the teeth that have been retained are then moved in the direction of the spaces created by the tooth removal. These two categories are a very gross division of orthodontic cases and there can be overlapping between them. For example, in a retraction case there may also be some expansion of teeth toward the periphery of a jaw to aid in the straightening. There are also other types of movements such as rotational movements, finishing movements, etc., that are routinely included in both expansion and retraction cases.
Conventional orthodontics is accomplished by moving the root of a tooth through its surrounding bone in the jaw of a patient. The bone of the jaw is similar to the long bones in one's arms and legs in that there is a hard outer shell, called the cortical plate or cortical bone, and a softer interior called the medullary bone. FIG. 1 shows a typical cross-section of a long bone in which a cortical plate 20 surrounds medullary bone 22.
The medullary bone has a good blood supply and is highly populated with pluripotential cells that can convert to osteoclasts that resorb old bone and osteoblasts that make new bone. It is this vital nature of the medullary bone which gives it the ability to respond in a dramatic and timely fashion to physical insult, such as the forces used to move teeth. To move a tooth orthodontically, the root of the tooth must be moved through the bone surrounding the tooth. This is called the alveolar bone, which consists of the medullary bone as well as the surrounding cortical plates which comprise the upper and lower jaws, also called dental arches. The alveolar bone remodels around a tooth being moved in response to pressure from one side of the tooth, as the tooth is being pressed against the alveolar bone on that side during movement, and in response to tension from the opposite side of the tooth as the tooth tends to move away from the alveolar bone on that side. Theoretically, in the course of this bone remodeling process, bone resorption, that is a loss of bone, occurs on the pressure side of the root surface in the direction in which the tooth is being moved. Bone deposition, also called apposition or new bone formation or build-up, takes place on the tension side of the root surface, that is the direction away from which the tooth is being moved.
Conceptually, it would seem that the roots of the teeth should move rapidly during conventional orthodontic treatment since they extend down into the jawbone and would seemingly be surrounded by the softer and more vital medullary bone. FIG. 2 shows a cross section of an upper front tooth comprising central incisor 24 having an orthodontic appliance such as a bracket 25 installed on it. The central incisor 24 is surrounded by a periodontal ligament 26 which attaches the root of the tooth to the alveolar bone. The medullary bone 22 is covered by the cortical plate 20, which is turn is covered by gum or gingival tissue 28.
Unfortunately, the root of a typical tooth 24 is usually so large in diameter that it takes up most of the space between the lingual cortical plate on the inside of the jaw and the facial cortical plate on the outside of the jaw. This is especially true with respect to the anterior teeth, that is teeth in the front of the mouth. Little, if any, room is left for the soft inner, medullary bone. As a result, much of the root of a tooth is covered with the hard cortical plate and with very little soft medullary bone as is shown in FIG. 3. Compared to medullary bone, the cortical plate has a greatly reduced blood supply and a negligible complement of pluripotential cells. This greatly reduces the ability of the cortical plates to remodel during the course of orthodontic treatment.
To maintain the same initial thickness of the alveolar bone over the inside and outside prominences of the root during the tooth movement, the corresponding inner and outer surfaces of the alveolar bone must thicken and thin, respectively. Thus as the alveolar bone adjacent to the pressure side of the root surface resorbs and the alveolar bone adjacent to the tension side of the root surfaces builds-up, the corresponding inner and outer surfaces of the alveolar bone must thicken and thin, respectively, as shown in FIG. 4. The arrows 30 indicate the direction in which the tooth is being moved. The dots, some of which are marked 32, indicate areas where the bone is being resorbed. The dark areas 34 indicate where new bone is being formed. Unfortunately, this process does not always occur as predictably as desired.
Recent studies have shown that when a tooth is moved a significant distance there is a tendency to lose the alveolar bone over the prominence of the root especially in the direction in which the tooth is being moved. This tendency to lose alveolar bone and to consequently expose the surface of the root of a tooth is called dehiscence formation. See, by way of example, a study by Jan L. Wennstrom entitled "Mucogingival Considerations in Orthodontic Treatment," published in Seminars in Orthodontics, Vol. 2, No. Mar. 1, 1996: pgs. 46-54; a study by G. G. Steiner, et al., entitled "Changes of the Marginal Periodontium as a Result of the Labial Tooth Movement in Monkeys," Journal Periodontal, June, 1981, pp. 314-20; "Mandibular Incisors, Alveolar bone and Symphysis After Orthodontic Treatment. A Retrospective Study," by Heinrich Wehrbein, et al., published in American Journal of Orthodontics and Dentofacial Orthopedics, September 1996, pp. 239-46.
As shown in FIG. 5, this loss of alveolar bone over the prominence of the root, or dehiscence formation, is particularly significant near the neck of a tooth 35 where the root is usually the widest in diameter and the overlying cortical plate is likely to be thin. The above studies have shown that the periodontal ligament and the alveolar bone recede along the prominence of the root to an area 33 more apical, that is toward the tip of the root of the tooth, than is normal. Thus, gum or gingival tissue 28 covers the root of the tooth without having any alveolar bone between it and the tooth. In other words, in the direction the tooth is being moved, the tooth is literally pushed into a position outside the periphery of the jaw bone. This results in a decrease in bony support for the tooth.
The potential for a dehiscence formation is more of a problem with teeth undergoing orthodontic treatment that are overlapped and crowded as shown in FIG. 6. To correct the crooked alignment of the teeth 29, the teeth must be expanded or moved toward the outside of the jaw, as shown by the arrows 30, to make room for them. FIG. 7 shows the final position of the teeth 29 after they have been straightened. The incisors 36 and 38, the premolar 40 and the molars 42 and 44 may all be moved facially, or outward, from their starting positions in FIG. 6 to their final position in FIG. 7 to complete the straightening process. Each of these teeth is susceptible to developing a dehiscence as shown in FIG. 5 where the alveolar bone has migrated apically over the prominence of the root.
Another undesirable sequela that can occur as a consequence of conventional orthodontics is referred to as apical root resorption. Apical root resorption refers to a situation in which the tip of the root resorbs. This root resorption can vary from slight to severe. As a result the root is shorter following the completion of the orthodontic work. Apical root resorption is a function of not only pressure but time. That is to say, the longer it takes to complete the orthodontic work, the more root resorption that can potentially be expected. One can typically expect to see more root resorption in an adult than in an adolescent. As an individual ages, there is often more of a tendency for the root to resorb in preference to the bone which surrounds it. This is generally attributed to the fact that with aging the cortical plates tend to thicken and even the medullary bone tends to become less vital, that is the blood supply decreases, and the marrow spaces become smaller and the fat content increases.
FIG. 8 shows a typical single-rooted tooth prior to having undergone orthodontic movement. Note the length of the tooth from its apex 46 to the tip 48 of its crown. FIG. 9 shows a reported condition of a tooth some time after it has undergone conventional orthodontic movement. Note that apical root resorption has significantly decreased the distance between the apex 46a of this tooth and the tip 48a of its crown. This has resulted in an unfavorable crown-to-root ratio. The length of the crown is now greater than the length of the root. Severe root resorption can lead to irreversible mobility of the teeth and at times even the loss of the teeth themselves. Apical root resorption as a result of conventional orthodontics was reported by Naphtall Brezniak, et al. in the American Journal of Orthodontics and Dentofacial Orthopedics, Vol. 103, No. 2, beginning at p. 62 in an article entitled "Root Resorption After Orthodontic Treatment: Part 1. Literature Review", and continuing at p. 138 in an article entitled "Root Resorption After Orthodontic Treatment: Part 2 Literature Review."
For orthodontic treatment to be considered successful, the completed case must remain stable. If in the years that follow the completion of the orthodontic work the teeth move and become crooked again, the case is considered to have relapsed. If a case relapses, all of the time and money that was invested in the orthodontic treatment was wasted. Orthodontic relapse is not an uncommon problem, especially when expansion is used to accomplish the desired major orthodontic movements. It has been stated that adequate root length and adequate bony support around the roots are important factors in the maintenance of post-treatment stability. See, by way of example, "Review of the Retention Problem," by R. Riedel, American Journal of Orthodontics, Vol. 30, 1960, pp. 179-99: and Edgewise Orthodontics. 2nd ed. St. Louis: The C.V. Mosby Company, R. C. Thurow, 1966, pp. 258-74. It has also been suggested that there may indeed be a relationship between orthodontic relapse and the parameters of increased root resorption. See, by way of example, "Orthodontic Relapse, Apical Root Resorption, and Crestal Alveolar Bone Levels," by Wendy Sharpe, et al., American Journal of Orthodontics and Dentofacial Orthopedics, Vol. 91, No. 3, 1987, pp. 252-58. Both apical root resorption and dehiscence formation result in less root surface in the bone at the completion of conventional orthodontic work than was present prior to starting the orthodontic work. Consequently, with less alveolar bone supporting the roots of the teeth, there is an increased risk that the completed case will relapse and fail.
Dehiscence formation not only predisposes a tooth to relapse, but it also predisposes a tooth to gingival recession. If due to a dehiscence forming there is now a lack of alveolar bone between the gingiva and the adjacent root surface, there is an increased tendency for the gingiva to recede, thereby exposing the root of the tooth. See, by way of example, "Mucogingival Considerations in Orthodontic Treatment" by Wennstrom, above, at p. 50; "Changes in Marginal Periodontium as a Result of the Labial Tooth Movement in Monkeys," by Steiner, et al., above, at pp. 317-20; and "Mucogingival Orthodontic and Periodontal Problems," by George V. Newman, et al., American Journal of Orthodontics and Dentofacial Orthopedics, Vol. 105, No. 4, April 1994, pp. 321-27.
A major drawback to conventional orthodontics is the long treatment time during which braces must be worn, which generally ranges from one to three years. Wearing braces for this period of time, is neither pleasant nor popular. Unfortunately, for reasons such as perceived social restrictions, many adults and adolescents alike decline orthodontic treatment. Those patients who accept treatment almost always look longingly to the day when their braces will be removed. The most frequent question asked of any orthodontist is, "When will my braces be taken off." Thus, shortening orthodontic treatment durations is desirable if it can be accomplished without jeopardizing the quality of the final result. Several attempts have been made to shorten the treatment time but have not adequately addressed the problem of dehiscence formation in the bone over the prominences of the roots as a consequence of orthodontic treatment.
A surgical procedure called corticotomy has been employed for several decades to attempt to shorten orthodontic treatment times. But corticotomy has been reported to have been used only following the cessation of growth in post-adolescents and adults. For the purpose of consistency and clarity the use of the term osteotomy will indicate a bony cut that extents through the entirety of the portion of the jawbone supporting a tooth, that is alveolus. This would include the outer or facial cortical plate, the softer inner medullary bone, and inside or lingual cortical plate. The term corticotomy will indicate a bony cut or perforation that extends through the entire thickness of the cortical plate of the alveolus and just barely into the underlying medullary bone. If there is no medullary bone under the cortical plate, a corticotomy will also refer to a bony cut or perforation that extends through most of the thickness of the cortical plate, but not its entire thickness. The lack of medullary bone is often encountered over the prominences of the roots, especially of the anterior or front teeth, and more so closer to the necks of the teeth where the roots are widest in diameter.
In the journal Oral Surgery, Oral Medicine and Oral Pathology, Vol. 12, May 1959, at page 515, Dr. H. Kole wrote an article entitled "Surgical Operations on the Alveolar Ridge to Correct Occlusal Abnormalities" in which he describes the use of the corticotomy in orthodontic tooth movement in humans. There are other references in the literature dating back to the late 1800's, but Kole is generally credited with the introduction of this procedure. Kole emphasized that the main resistance to tooth movement is encountered in the continuous cortical layer. He suggested that this is likely attributable to the slower remodeling process in the cortical bone as compared to the much faster remodeling capabilities of the medullary bone. He reasoned that by disrupting the continuity of the cortical layer, the speed of the tooth movement could be greatly increased. To gain access to the cortical layer of bone, it was necessary to reflect full thickness gingival, or mucoperiosteal, flaps. But in doing so, the blood supply from the overlaying mucoperiosteum was disrupted. Kole speculated that by leaving medullary bone mostly intact, it would act as the nutritive pedicle, that is a vascular pathway, to the denuded bone and prevent an avascular phenoma, or lack of blood flow leading to necrosis, in the surgerized alveolar bone. Kole's objective was to create blocks or segments of bone in which a tooth or group of teeth was embedded and which were connected to each other and to other structures through only the medullary bone. In a manner of speaking, the crowns of the teeth then became the handles by which the segments of bone could be moved somewhat independently of each other with the applied orthodontic forces. He theorized that the rapid tooth movement that resulted was due to the lack of resistance of the soft medullary bone.
However, when Kole introduced the corticotomy it was used in conjunction with osteotomies in both expansion and retraction scenarios. To promote expansion of the teeth toward the periphery of the outline of the jaw, he made vertical and horizontal cuts in the alveolar process both facially arid lingually to create the bony blocks or segments. The vertical cuts were made interdentally, that is between the teeth, and were done in the manner of a corticotomy. That is, these cuts penetrated the entire thickness of the cortical layer and extended only barely into the medullary bone. The vertical cuts started interproximally between the crowns of adjacent teeth and extended well beyond the apices of the teeth. These vertical cuts were then joined beyond the apices with a horizontal cut. The horizontal cut, however, was performed in the manner of an osteotomy, that is to say that it penetrated the entire thickness of the alveolus to include the facial cortical plate, the lingual cortical plate, and the interposed medullary bone. In the upper posterior areas, these horizontal osteotomies penetrated the Schneiderian membrane, which is the membrane which lines the maxillary sinuses. The only horizontal cut that was not performed in the manner of an osteotomy was in the lower posterior areas. The neural and vascular innervation of the lower posterior areas preclude such a cut. In the lower posterior areas the connecting horizontal cut was performed in the manner of a corticotomy. In retraction cases Kole utilized a wide vertical osteotomy in the extraction sites, leaving only a thin layer of medullary bone over the adjacent root surfaces. It appears that most of the orthodontic movements were accomplished with removable appliances that were to be worn continually and only removed briefly for cleaning.
Kole claimed that most of the cases were completed in 12 weeks or less. Upon examination of the cases he reported, it seems that the fine finishing movements that are typically employed today before an orthodontic case would be considered completed were absent. The orthodontic movements, which Kole completed in 12 weeks or less, were rather gross major movements.
Kole claimed that leaving the medullary bone intact prevented devitalization of the teeth and also prevented injury to the periodontium and pocket formation. He also attributed a lack of root resorption to the notion that it is not the tooth itself that was displaced, but rather the alveolar block in which the tooth was embedded. He also suggested that the healing of the cortical cuts should prevent relapse. It is most important to note that Dr. Kole makes no mention of luxation, or dislocation, of individual dentoalveolar blocks in an attempt to mobilize them.
In the Journal of Oral Surgery, volume 30, September 1972, pp. 640-48, William H. Bell and Barnet M. Levy wrote an article entitled "Revascularization and Bone Healing After Maxillary Corticotomies". In this article they questioned the appropriateness of the one-stage corticotomy procedure as presented by Kole in 1959. One-stage refers to the reflection of facial and lingual full thickness flaps in the same area during the same surgical procedure. They expressed concern that the resulting dentoalveolar blocks, which are for a short period of time deprived of the mucoperiosteal blood supply, might not receive an adequate blood supply through the rather small amount of remaining interconnecting medullary bone. To test their theory, one-stage maxillary corticotomies were performed bilaterally in the premolar and incisor regions in four rhesus monkeys. From their results, they concluded that the one-stage maxillary corticotomies had a disruptive effect on the maxillary central incisors. In particular there was a damaging effect to the periodontium around these teeth. It was noted that at nine weeks post-surgery, there was gross ischemia or a lack of oxygen carrying material of the blood supply due to the interruption of the blood supply, in much of the alveolar bone surrounding the coronal portion of the incisor roots and within the surrounding periodontal vascular plexuses.
Bell and Levy, however, did not follow the protocol as described by Kole. The vertical interdental cuts were corticotomies as described by Kole. But rather than connecting the vertical corticotomies beyond the apices of the teeth with a horizontal osteotomy, they used a corticotomy. Of most notable importance is that the resulting dentoalveolar segments were immediately mobilized by malleting a chisel between the corticotomy sites. Bell and Levy admitted that the immediate mobilization of each dentoalveolar segment likely replaced the corticotomies in a number of areas with complete interdental osteotomies. This would have most certainly had a negative effect on the circulation in these areas. Kole, as mentioned above, did not recommend the mobilization of the dental alveolar segments.
In the Journal of Maxillofacial Surgery, Volume 3, No. 2, 1975, pp. 81-4, Jurgen Duker wrote an article entitled "Experimental Animal Research into Segmental Alveolar Movement after Corticotomy" in which he repeated Kole's procedure fairly closely to the way it was described in 1959. Six male beagle dogs were utilized. Vertical corticotomies were preformed between the upper central incisors and upper lateral incisors. No vertical corticotomy was performed between the two upper central incisors. The two vertical corticotomies were then connected beyond the apices with a horizontal osteotomy. With the use of very thick rubber bands, the segment of bone with the two central incisors was displaced about 4 mm in 8-20 days. The rubber bands were attached to a heavy facial arch wire which also served to hold the upper lip away from the incisors during the segmental movement. The use of this type of device would not be practical in humans.
Duker did keep the vertical corticotomies somewhat shy of the marginal bone. He theorized that by doing so there would be less of a chance of damaging the marginal periodontium. He concluded that rapid movement performed in this manner does not damage the vasculature supplying the dental pulps. He further noted that clear vascular changes were found in the marginal gingiva. Duker also observed that two of the dogs had developed slightly deepened periodontal pockets. He felt that this was of minimal consequence and by keeping the vertical corticotomies short of the alveolar crest significant damage in this regard could be avoided. Like Kole, Duker did not report mobilization of the dentoalveolar segments by luxation.
H. Suya wrote a chapter entitled "Corticotomy in Orthodontics" at pp. 207-26 of Mechanical and Biological Basis in Orthodontic Therapy, edited by Drs. Ernst Hosl and Anton Baldauf and published by Huthig Book Vertag GmbH of Heidelberg, Germany in 1991. Dr. Suya first traced the history of corticotomy. He described corticotomy on page 208 of his chapter as a surgical technique "in which a fissure is made through the cortical bone (compact bone) that surrounds a tooth so that the tooth is embedded within a block of bone that is connected to adjacent blocks through only the medullary bone. In this way, the tooth plays the role of the handle by which the bands of less dense medullary bone are moved block-by-block. In other words, the orthodontic tooth movement in corticotomy is a process of moving blocks rather than moving only the teeth themselves."
At page 216 Suya described the orthodontic and surgical procedures involved in corticotomy-assisted orthodontics. This included securing the orthodontic brackets to the teeth prior to the surgical portion of the treatment. The actual surgery was initiated by intracrevicular incisions around the necks of the teeth with subsequent reflection of full thickness gingival flaps to gain access to the cortical bone overlying the roots of the teeth to be moved. He advocated not using vertical releasing incisions at the opposite ends of the flaps to prevent the trapping of air inside the flaps at the time of flap replacement and suturing. The cortical plates were completely exposed both facially and lingually beyond the apices of the teeth. The corticotomy cuts were a combination of vertical and horizontal grooves that were made both facially and lingually around the teeth to be moved. The vertical interdental cuts began 2 to 3 millimeters below the alveolar crest, as recommended by Duker, and extended beyond the apices of the teeth, as recommended by Kole. The horizontal cuts were made beyond the apices of the teeth and connected the interdental vertical cuts. In this respect Suya differed from Kole, who used a horizontal osteotomy rather than the horizontal corticotomy, except on the facials of the lower posterior teeth where Kole also used a horizontal corticotomy.
In paragraph 7 on page 216 Suya stated: "These resections are made on both facial and lingual sides so that the block of bone thereby created, is now retained by only medullary bone. Resistance to the tooth movements is now obviously reduced." At the conclusion of the surgery the full thickness gingival flaps were returned to their original positions and secured by continuous suture. In all examples given Suya performed the surgery at two different sittings, that is, the upper arch at one session and the lower arch at another session. Like Kole, Suya did not mobilize the resulting dentoalveolar segments by luxation. Suya inserted and activated the archwire connected to the brackets on the teeth immediately following the completion of the surgery. A packing material dripping with disinfectant was then placed around the necks of the teeth. Suya recommended making the periodic orthodontic adjustments at 10 to 14 day intervals until the treatment goal was accomplished. Suya claims to have treated hundreds of post-adolescent and adult Japanese patients since 1972. He reportedly limited the usage of the corticotomy assisted orthodontics to post-adolescents and adults, since in these patients the rapid growth period was ended and movement was limited to the dentoalveolar element. Suya reported that 69% of the time stage II orthodontic movements were completed within 127 days. Although Suya gave examples in which different malocclusions were treated, they were apparently all treated through expansion. He gave no examples in which extractions with subsequent retraction of the teeth were employed. Suya was insistent that the rapid tooth movement which followed the corticotomy surgery was attributable to the movement of the resulting dentoalveolar blocks and not to the movement of the teeth through the surrounding alveolar bone. Since in the "dentoalveolar block movement hypothesis" the tooth and the block of bone in which it was embedded were thought to move in unison, there was no expressed concern that the tooth was being moved to a position outside the periphery or limits of the alveolar bone, which would result in dehiscence formation over the prominences of the root. This set the stage for some erroneous assumptions, two of which were that the completed case would be more stable and that bone grafting was not needed. More specifically, in Table 7 on Page 210 of this chapter, Dr. Suya specifically states that corticotomy orthodontics "(N)egates the need for a bone grafting procedure." J. Milford Anholm, et al. reported in the California Dental Association Journal, Dec. 1986 edition, beginning at page 8, on research conducted at the Loma Linda University School of Dentistry on corticotomy in an article entitled "Corticotomy-facilitated Orthodontics." They traced a history of corticotomy procedures and credited their research in this field since 1983 to Dr. Suya's encouragement and assistance. The procedure that they described is substantially the same as that used by Dr. Suya. After explaining the vertical and horizontal cuts made in the cortical bone, Dr. Anholm, et al. stated "These resections are made both facially and lingually so that the tooth is now connected only through medullary bone and resistance to movement is greatly reduced." They gave one case report in which a 23 year old male with a severe malocclusion was treated by non-extraction and expansion. This case was completed in 11 months. They listed as one of the many unanswered questions about corticotomy-facilitated orthodontics "(H)ow much tooth movement is actually accomplished with the bone movement?" They reported that most orthodontic cases can be completed in a year or less with this method.
The research at Loma Linda University School of Dentistry was further reported by Bernard Gantes, et al., in an article entitled "Effects on the Periodontium Following Corticotomy-Facilitate Orthodontics, Case Reports," beginning at page 234 of Volume 4 of the April 1990 edition of the Journal of Periodontology. In the four adult cases that were used in the final statistical analysis, it appears that extractions with subsequent retraction were employed. As Kole recommended in 1959 the extraction sites were osteotomized to create spaces in which to move the adjacent teeth that were being retracted. Orthodontic forces were employed. They reported a mean treatment time of 14.8 months for their corticotomy-facilitated orthodontic patients, as compared with 28.3 months for the conventional orthodontic treatment controls. They reported no significant adverse clinical periodontal effects.
Gantes et al., did, however, report noticeable apical root resorption as evidenced on the post-treatment periapical radiographs. As indicated above, Dr. Suya did not report significant apical root resorption when treating cases with expansion. No additional information was provided by Gantes, et al., concerning the amount of tooth movement that was actually accomplished with segmental movement of the dentoalveolar blocks. Due to the increased appliance complexity and the frequency of patient visits, they estimated the total chair time for the corticotomy patients to be approximately the same as that for the conventional orthodontic controls.